1. Field of the Invention
This invention relates to methods for desiccating the foliage of food crops and, in particular, to methods for facilitating the harvest of food crops.
2. Introduction
A wide variety of food crop plants have abundant foliage which interferes with and increases the cost of crop harvest, particularly with mechanical harvesters. A variety of methods and compositions have been devised to desiccate foliage sufficiently to facilitate harvest. As used herein, "desiccating" is used in the agricultural sense which typically means reducing the above-ground biomass sufficiently to reduce interference with harvest rather than in the strict chemical sense of the word. In chemical terminology, desiccation usually connotes removal of water by chemical action. Sugar cane and other crops, the produce of which is not harmed by fire, have been flame-defoliated, although this procedure now is banned in a many areas to control air pollution. A variety of chemical desiccants have been employed to reduce the mass and improve the manageability of crop plant foliage. Illustrative are sodium chlorate, endothall, arsenic acid, and secondary butyl-2,4-dinitrophenol sold as Dinoseb.RTM., Synox.RTM., and under other designations.
Sulfuric acid applied at sufficiently high dosage rates desiccates crop vegetation, but the use of sufficiently strong sulfuric acid at sufficiently high rates presents several significant problems. Sulfuric acid damages the harvestable portion of many crops by oxidation and/or dehydration reactions characteristic of sulfuric acid. Furthermore, sulfuric acid dosage rates required to achieve rapid foliage desiccation are substantial since the acid is consumed by reaction with foliage by oxidation and/or dehydration, and the hazards associated with the use of large volumes of concentrated sulfuric acid are well known and require great care in application, sophisticated, expensive application equipment, and protective personnel clothing and devices. Furthermore, the use of such volumes of sulfuric acid can result in soil over-acidification and ecotoxic effects associated with acid run-off. Other chemical harvesting aids, such as the desiccants mentioned above, also suffer from one or more disadvantages. Several are relatively expensive, and all are potentially toxic. Some are translocated to the harvestable portion of food crops with obvious, undesirable effects. For instance, arsenic acid is very toxic both to plants and the environment and can contaminate both the harvestable food product and the environment. Sodium chlorate results in the addition of both sodium and chlorine to the crop and soil, both of which are undesirable. It is also explosive and difficult to handle. Secondary butyl-2,4-dinitrophenol has been identified, in recent studies, as a carcinogen, oncogen, and teratogen. The relatively slow activity of several of the chemical desiccants is also disadvantageous since it is generally desirable to harvest the crop as soon as possible after preharvest treatment, i.e., within 24 hours or less. However, some harvest aids, such as secondary butyl-2,4-dinitrophenol require days or weeks to desiccate plant foliage sufficiently to facilitate harvest, depending upon the crop type and field conditions. Furthermore, the residual toxicity of several chemical harvest aids prevents entry of personnel into treated fields due to toxic chemical residue on plant foliage.
The desirability of harvesting as soon as possible after preharvest treatment is due to several factors, and potatoes and sugar beets are classic illustrations. In these and other crops, it is preferable to foster productive growth of the crop until harvest. Destruction of plant foliage obviously deters or terminates that process, and the lapse of any significant time between preharvest treatment and harvest results in a proportionate economic loss to the grower and increases the risk of crop spoilage.
Accordingly, a need exists for a nontoxic, fastacting, relatively inexpensive harvest aid that rapidly desiccates living food crop foliage sufficiently to facilitate harvest.